Rolling/sliding member, toroidal continuously variable transmission using the same method of manufacturing rolling/sliding member

ABSTRACT

A rolling/sliding member used for a toroidal continuously variable transmission according to the present invention is made of steel containing at least C: not less than 0.8 wt % and not more than 1.5 wt %, Si: not less than 0.9 wt % and not more than 2.1 wt % and Cr: not less than 2 wt % and not more than 5 wt %, and by applying surface hardening through machining to a surface whose surface hardness is set to not less than 60 HRC and not more than 64 HRC through quenching/tempering, surface compression residual stress thereof is set to not less than 700 MPa and not more than 1100 MPa. Furthermore, the amount of reduction of surface hardness when heated at 300° C. is set to not more than 1 HRC.

FIELD OF THE INVENTION

The present invention relates to a rolling/sliding member used for atransmission of an automobile or the like, a toroidal continuouslyvariable transmission using this rolling/sliding member and a method ofmanufacturing the rolling/sliding member.

DESCRIPTION OF THE PRIOR ART

A toroidal continuously variable transmission is provided with an inputdisk and an output disk each having a concave curved raceway surface tobe a roller raceway surface on a side thereof and a roller which makesrolling/sliding contact with the raceway surfaces of both disks facingeach other under a lubricated and high-pressure condition. The toroidalcontinuously variable transmission can transmit torque between the disksby means of traction between each disk and the roller and canincrease/decrease the number of revolutions (change gear ratio) of theoutput disk with respect to the input disk with smooth motion which isdifferent from motion of a conventional transmission by adjusting theposition at which the roller contacts each disk.

In the above described toroidal continuously variable transmission,rolling/sliding members which make rolling/sliding contact such as theinput and output disks and roller make rolling/sliding contact with eachother in a condition in which they are exposed to high temperature, highcontact pressure and moreover shear stress which acts through tractionduring torque transmission, and they are therefore under extremeoperating conditions. For this reason, high fatigue resistance isrequired so as to reduce the possibility of producing flaking caused bysurface flaking and a structural variation with micro cracks or the likeproduced on the surface as starting points.

To meet such requirements, in manufacturing rolling/sliding members of atoroidal continuously variable transmission, there is a proposal of atechnique as described in Japanese Patent Laid-Open No. 2004-218715 forperforming quenching/tempering processing on a raw material made ofbearing steel, and then performing shot peening treatment and vanishprocessing to apply compression residual stress of the surface of theraw material to 600 to 1000 MPa.

In the above described conventional example, compression residual stressapplied to the surface increases fatigue resistance and can therebysuppress surface originated flaking. This makes it possible to preventearly damage on the surface and acquire a high degree of durability.

However, there is an increasing demand for a reduction of fuelconsumption and downsizing of automobiles in recent years and there isalso an increasing demand for a higher degree of durability of atransmission used for such automobiles to meet the demand for downsizingthereof.

OBJECT AND SUMMARY OF THE INVENTION

It is an object of the present invention to provide a rolling/slidingmember capable of achieving greater durability and a toroidalcontinuously variable transmission using this rolling/sliding member anda method of manufacturing the rolling/sliding member.

In order to attain the above described object, the inventors have madeevery effort to research in pursuit of development of a rolling/slidingmember capable of realizing greater durability. In the process, theinventors have conducted various experiments and research focusing on areduction of surface hardness resulting from heat generation tempering(heating) due to rolling/sliding contact, which is one of causes forsurface cracks. As a result, the inventors have come up with the presentinvention by discovering that especially the contents of Si, Crcontained in the raw material of a rolling/sliding member andcompression residual stress of the surface have a great influence on thereduction of surface hardness due to heating.

That is, the present invention is a rolling/sliding member used for atoroidal continuously variable transmission, wherein the rolling/slidingmember is made of steel containing at least:

C: not less than 0.8 wt % and not more than 1.5 wt %

Si: not less than 0.9 wt % and not more than 2.1 wt %

Cr: not less than 2 wt % and not more than 5 wt %

wherein by applying surface hardening through machining to a surfacewhose surface hardness is set to not less than 60 HRC and not more than64 HRC through quenching/tempering, surface compression residual stressthereof is set to not less than 700 MPa and not more than 1100 MPa andthe amount of reduction of surface hardness when heated at 300° C. isnot more than 1 HRC.

According to the rolling/sliding member in the above describedconstruction, steel containing the above described predetermined amountsof Si and Cr is used, quenching and tempering are performed to therebyset predetermined surface hardness and the above described surfacecompression residual stress is added, and it is thereby possible to setthe amount of reduction of surface hardness when heated at 300° C. tonot more than 1 HRC.

The temperature of the contact surface of the rolling/sliding memberused for the toroidal continuously variable transmission is known togenerally increase to approximately 200 to 300° C. throughrolling/sliding thereof. In contrast, even when the surface of therolling/sliding member is heated, the reduction of surface hardness issuppressed to not more than 1 HRC, and therefore even when the surfaceof the rolling/sliding member is heated by heat generation accompanyingrolling and sliding, it is possible to suppress the reduction of surfacehardness. Therefore, it is possible to keep surface hardness necessaryfor the rolling/sliding member and suppress generation of surface cracksoriginating from the reduction of surface hardness. In addition tocompression residual stress applied to the surface, it is possible toeffectively enhance fatigue resistance of the rolling/sliding member andobtain higher durability.

Furthermore, the amount of retained austenite before the surfacehardening is preferably not less than 10 wt % and not more than 20 wt %.

When the amount of retained austenite exceeds 20 wt %, retainedaustenite is decomposed through heat generation accompanying rolling andsliding of the rolling/sliding member and surface flaking is more likelyto occur as a consequence.

Since fatigue resistance to rolling and sliding generally improves bycontaining a certain amount of retained austenite in steel, it ispossible to increase the fatigue resistance by setting the amount withinthe above described range without producing surface flaking or the like.

Furthermore, the above described rolling/sliding member preferably hasan austenitizing temperature of not less than 870° C. and not more than950° C. and an tempering temperature of not less than 200° C. and notmore than 280° C.

When the above described austenitizing temperature is lower than 870°C., predetermined surface hardness may not be obtained. On the otherhand, when the austenitizing temperature is higher than 950° C.,austenite crystal grains during quenching may become coarse and thestrength of the rolling/sliding member after quenching and tempering maydecrease.

Furthermore, the present invention is a method of manufacturing arolling/sliding member used for a toroidal continuously variabletransmission, comprising a quenching/tempering process of performingquenching/tempering on an intermediate material of the rolling/slidingmember made of steel containing at least:

C: not less than 0.8 wt % and not more than 1.5 wt %

Si: not less than 0.9 wt % and not more than 2.1 wt %

Cr: not less than 2 wt % and not more than 5 wt %

at an austenitizing temperature of not less than 870° C. and not morethan 950° C. and an tempering temperature of not less than 200° C. andnot more than 280° C. to thereby set surface hardness of theintermediate material to not less than 60 HRC and not more than 64 HRCand the amount of retained austenite to not less than 10 wt % and notmore than 20 wt % and a surface hardening process of applying surfacehardening through machining to the intermediate material which hasundergone the quenching/tempering process, thereby setting surfacecompression residual stress of the intermediate material to not lessthan 700 MPa and not more than 1100 MPa and setting the amount ofreduction of surface hardness to not more than 1 HRC when heated at 300°C.

According to the method of manufacturing a rolling/sliding member in theabove described construction, surface hardness is set to 60 HRC to 64HRC and the amount of retained austenite is set to not less than 10 wt %and not more than 20 wt % by quenching and tempering an intermediatematerial made of steel with the above described predetermined contentsof Si and Cr and this intermediate material is further subjected tosurface hardening through machining, and it is thereby possible to applysurface compression residual stress within a range of not less than 700MPa and not more than 1100 MPa and set the amount of reduction ofsurface hardness when heated at 300° C. to not more than 1 HRC.

The rolling/sliding member manufactured in this way can keep surfacehardness necessary for the rolling/sliding member even when the surfaceof the rolling/sliding member is heated by heat generation accompanyingrolling and sliding and suppress generation of surface cracks caused bythe reduction of surface hardness. In addition to compression residualstress applied to the surface, it is further possible to effectivelyenhance fatigue resistance of the rolling/sliding member.

That is, according to the above described method of manufacturing arolling/sliding member, it is possible to effectively increase fatigueresistance and obtain a rolling/sliding member having higher durability.

Furthermore, the present invention is a toroidal continuously variabletransmission including an input disk having a concave curved racewaysurface on a side, an output disk having a concave curved racewaysurface facing the raceway surface of the input disk on a side androllers which are sandwiched between raceway surfaces of the respectivedisks in a rotatable manner and transmit torque between the respectivedisks through rolling and sliding between the respective disks, whereinat least one of the input disk, output disk and rollers, which arerolling/sliding members, is the above described rolling/sliding member.

According to the toroidal continuously variable transmission in theabove described construction, since each of the above described disksand rollers is the above described rolling/sliding member, it ispossible to effectively increase fatigue resistance of these members andfurther enhance durability of the toroidal continuously variabletransmission.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram showing a variator part of a full toroidalcontinuously variable transmission which is a kind of a toroidalcontinuously variable transmission according to an embodiment of thepresent invention;

FIG. 2 shows manufacturing processes of both disks and the roller;

FIG. 3 is a schematic diagram of a durability tester used for averification test; and

FIG. 4 is a graph showing a relationship between the amount of Si andthe amount of Cr contained in steel of products according to differentexamples and comparative examples.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Next, a preferred embodiment of the present invention will be explainedwith reference to the attached drawings. FIG. 1 is a schematic diagramshowing a variator part of a full toroidal continuously variabletransmission which is a kind of a toroidal continuously variabletransmission according to an embodiment of the present invention. Thisvariator 1 is provided with an input shaft 3 which is driven to rotateby an output shaft 2 of an engine and input disks 5 are supported in thevicinity of both ends thereof.

A concave curved raceway surface 5 b is formed in one side of each inputdisk 5 and a spline hole 5 a with a plurality of grooves is formed in aninner circumference thereof. The input disk 5 is joined to the inputshaft 3 in an integrally rotatable manner by coupling the spline hole 5a with a spline shaft 3 a provided in the input shaft 3. Furthermore,the movement of the respective input disks 5 in a direction of movingaway from each other is regulated by an engagement ring 51 fixed to theinput shaft 3.

An output section 6 provided with output members 6 a and output disks 6b which are supported by the output members 6 a in an integrallyrotatable manner is provided in the center of the input shaft 3 in theaxial direction in a relatively rotatable manner with respect to theinput shaft 3. A concave curved raceway surface 6 c is formed in oneside of the output disk 6 b facing the raceway surface 5 b of the inputdisk 5. Sprocket gears 6 e which engage with a chain 6 d are formed onthe outer circumference of the output members 6 a so that power istransmitted to the outside via the chain 6 d.

The output disk 6 b is joined to the output member 6 a in such a mannerthat the output disk 6 b is allowed to inch in the axial direction, agap 6 g is provided on the back thereof and a backup plate 6 h isarranged. The gap 6 g is sealed by a casing 6 f and a seal (not shown)and supplying a hydraulic pressure to this gap 6 g from a hydraulicpower source 9 puts force on the output disk 6 b in the direction of theopposing input disk 5 and applies a predetermined terminal load thereto.

The space between the raceway surface 5 b of the input disk 5 and theraceway surface 6 c of the output disk 6 b facing each other isstructured as a toroidal gap, this toroidal gap is supplied with alubricant (traction oil) and three disk-shaped rollers 7 which rotatewhile making rolling/sliding contact with each raceway surface 5 b, 6 cvia an oil film are arranged equiangularly on the circumference of acircle. The parts that contact the raceway surfaces 5 b and 6 c areouter surfaces 7 b of the roller 7. Each roller 7 is supported by acarriage 8 in a rotatable manner such that an axis of rotation 7 athereof can be tilted. A drive force by a hydraulic pressure is appliedto the carriage 8 in a direction crossing the surface of the sheet inFIG. 1.

In the variator 1, when the pair of input disks 5 rotate, torque istransmitted from the input disks 5 to the output disks 6 b via the threerollers 7 on the left and right sides by a shear force of the oil film.The rollers 7 supported by the carriage 8 tilt the axis of rotation 7 ato cancel unbalance between a reaction force produced in the carriage 8by transmitting the torque and the torque required to drive the outputdisk 6 b. This causes the positions of the rollers 7 to change as shownby two-dot dashed lines in the figure and causes the change gear ratiobetween the both disks 5, 6 b to change continuously.

In the full toroidal continuously variable transmission in the abovedescribed construction, the both disks 5, 6 b and the rollers 7 arerolling/sliding members which make rolling/sliding contact with eachother and the rolling/sliding member according to the present inventionis applied thereto. These rolling/sliding members (both disks 5, 6 b,rollers 7) are made of heat-resistant bearing steel. This heat-resistantbearing steel is adjusted to a composition containing alloy elementswithin a range satisfying C: not less than 0.8 wt % and not more than1.5 wt %, Si: not less than 0.9 wt % and not more than 2.1 wt %, Mn: notless than 0.05 wt % and not more than 0.5 wt %, Cr: not less than 2 wt %and not more than 5 wt %, and Mo: not less than 0.05 wt % and not morethan 0.5 wt % with the remainder being Fe and unavoidable impurities.

In the above described heat-resistant bearing steel, when the content ofC is less than 0.8 wt %, sufficient hardness may not be obtained afterquenching. For this reason, the content of C needs to be not less than0.8 wt %. On the other hand, when the content of C exceeds 1.5 wt %,toughness decreases and results in a decrease of strength, and thereforethe content of C needs to be not more than 1.5 wt %.

Furthermore, the content of C of the above described heat-resistantbearing steel is preferably not less than 0.9 wt % in the abovedescribed range. Furthermore, the content of C is preferably not morethan 1.1 wt % in the above described range.

Moreover, in the above described heat-resistant bearing steel, apredetermined amount of Si needs to be contained for the purpose ofsuppressing decrease of the value of hardness when heated to not lessthan 300° C., increasing tempering softening resistance and therebyincreasing high-temperature strength.

When the content of Si is less than 0.9 wt %, the stability of retainedaustenite becomes insufficient and heat-resistance of the materialbecomes insufficient, and therefore the content of Si needs to be notless than 0.9 wt %. Furthermore, when the content of Si exceeds 2.1 wt%, toughness decreases and results in a decrease of strength, andtherefore the content of Si needs to be not more than 2.1 wt %.

Furthermore, the content of Si of the above described heat-resistantbearing steel is preferably not more than 1.7 wt % in the abovedescribed range.

In the above described heat-resistant bearing steel, Cr is an elementwhich influences the formation of carbide and hardenability.

When the content of Cr is less than 2 wt %, the strength of the abovedescribed heat-resistant bearing steel decreases, and therefore thecontent of Cr needs to be not less than 2 wt %. When the content of Crexceeds 5 wt %, workability decreases due to an influence of carbide,and therefore the content of Cr needs to be not more than 5 wt %.

In the above described heat-resistant bearing steel, since Mn improveshardenability of steel, secures sufficient hardness of steel andeffectively acts on improvement of rolling fatigue life, the content ofMn needs to be not less than 0.05 wt %. Furthermore, when the content ofMn exceeds 0.5 wt %, machinability and toughness decrease, and thereforethe content of Mn needs to be not more than 0.5 wt %.

Furthermore, the content of Mn in the above described heat-resistantbearing steel is preferably not less than 0.4 wt % in the abovedescribed range.

Mo is an element which improves the wear resistance throughstabilization of residual carbide. The content of Mo being not less than0.05 wt % increases hardenability, contributes to improvement ofstrength after quenching/tempering, improves wear resistance and rollingfatigue life through deposition of stable carbide, but since thisoperation and effect saturate at 0.5 wt %, the content of Mo is set tonot more than 0.5 wt %.

Furthermore, the content of Mo in the above described heat-resistantbearing steel is preferably not less than 0.3 wt % in the abovedescribed range.

Next, a method of manufacturing the both disks 5, 6 b, and the rollers 7described above will be explained. FIG. 2 shows manufacturing processesof the both disks 5, 6 b, and the rollers 7. In the figure, anintermediate material of the both disks 5, 6 b, and the rollers 7 isformed out of a raw material made of the above described heat-resistantbearing steel through hot forging and cutting or the like (step S1).

The intermediate material formed in step S1 is subjected to quenchingand tempering at an austenitizing temperature of not less than 870° C.and not more than 950° C. and at an tempering temperature of not lessthan 200° C. and not more than 280° C. (quenching/tempering process,step S2). Through this quenching/tempering process, surface hardness ofthe intermediate material becomes not less than 60 HRC and not more than64 HRC and the amount of retained austenite becomes not less than 10 wt% and not more than 20 wt %.

When the austenitizing temperature is lower than 870° C., predeterminedsurface hardness may not be obtained. On the other hand, when it ishigher than 950° C., austenite crystal grains become rough duringquenching and the strength of the rolling/sliding members afterquenching and tempering may decrease. For this reason, the austenitizingtemperature is preferably set to not less than 870° C. and not more than950° C.

Furthermore, the above described austenitizing temperature is preferablyset to not more than 920° C. within the above described range. Settingthe austenitizing temperature to not more than 920° C. can furtherreduce austenite crystal grains and thereby inhibit carbide fromreducing and suppress the reduction of toughness and suppress thereduction of strength.

Next, the intermediate material which has undergone step S2(quenching/tempering process) is subjected to surface hardening throughmachining such as shot peening treatment (step S3, surface hardeningprocess). This surface hardening process causes surface compressionresidual stress of the intermediate material to be not less than 700 MPaand not more than 1100 MPa and causes the amount of reduction ofhardness when heated at 300° C. to be not more than 1 HRC.

The intermediate material which has undergone the surface hardeningprocess is subjected to predetermined finishing (step S4) and the bothdisks 5, 6 b, and the rollers 7 can thereby be obtained as finishedproducts.

The both disks 5, 6 b, and the rollers 7 manufactured as shown aboveundergo the quenching/tempering process and the surface hardeningprocess and surface hardness thereof is thereby set to not less than 60HRC and not more than 64 HRC, the amount of retained austenite is set tonot less than 10 wt % and not more than 20 wt %, surface compressionresidual stress thereof is set to not less than 700 MPa and not morethan 1100 MPa by applying surface hardening to the surface throughmachining such as shot peening treatment and the amount of reduction ofsurface hardness when heated at 300° C. can be set to not more than 1HRC.

In this embodiment, the above described surface hardness and amount ofretained austenite can be obtained by performing the above describedquenching/tempering process on the heat-resistant bearing steel, butwhen surface hardness of the above described intermediate material issmaller than 60 HRC, the strength may fall short of the strengthnecessary for the rolling/sliding member, which increases thepossibility that surface flaking may occur. Furthermore, when surfacehardness of the raw material exceeds 64 HRC, toughness of the membersdecreases, which may cause the members to fracture or crack when used.

Furthermore, when the content of retained austenite in steel reaches acertain amount, fatigue resistance against rolling and sliding improves.However, when the amount of retained austenite is excessive, heatgenerated by rolling and sliding may cause retained austenite todecompose and increase the possibility that surface flaking may occur asa consequence, and therefore the amount of retained austenite ispreferably set to not more than 20 wt % as described above.

Furthermore, in this embodiment, the heat-resistant bearing steel issubjected to the quenching/tempering process and compression residualstress is then applied through shot peening treatment, and this isattributable to the fact that machining (shot peening treatment) causesretained austenite to be transformed to martensite. For this reason,when the amount of retained austenite is too little, it is not possibleto secure sufficient compression residual stress when subjected tomachining, and therefore the amount of retained austenite is preferablyset to not less than 10 wt %.

Furthermore, though compression residual stress of the surface of therolling/sliding members after shot peening treatment is set to not lessthan 700 MPa and not more than 1100 MPa, when this compression residualstress is less than 700 MPa, fatigue resistance may fall short of thefatigue resistance necessary for the rolling/sliding members. On theother hand, when the compression residual stress is greater than 1100MPa, excessive plastic deformation may occur on the surface of theintermediate material, making the rolling/sliding members brittle andthis may cause surface flaking.

In this embodiment, the amount of reduction of surface hardness of therolling/sliding member after shot peening treatment when heated at 300°C. is set to not more than 1 HRC, and when the amount of reduction ofsurface hardness is greater than 1 HRC, surface hardness of therolling/sliding members decreases along with rolling and sliding, whichmay cause cracks on the surface.

This is because the temperature at the contact surface of arolling/sliding member used for the toroidal continuously variabletransmission is generally known to increase up to approximately 200 to300° C. through rolling and sliding and the rolling/sliding member isalways heated at around the above described temperature when thetransmission is in operation. When heated at 200 to 300° C. in this way,the surface of the rolling/sliding member set to predetermined surfacehardness in the quenching/tempering process is tempered, which may causethe surface hardness to decrease considerably. That is, when the amountof reduction of surface hardness when heated at 300° C. is greater than1 HRC, the reduction of surface hardness increases, the strength fallsshort of the strength necessary for the rolling/sliding member, whichmay produce cracks on the surface. On the other hand, as in the case ofthis embodiment, when the amount of reduction of surface hardness whenheated at 300° C. is set to be smaller than 1 HRC, even when the surfaceis heated, it is possible to prevent the surface hardness fromdecreasing considerably.

The full toroidal continuously variable transmission according to thisembodiment is intended to synergistically increase fatigue resistanceeffectively and further increase durability by defining the compositionof steel used for the rolling/sliding members (both disks 5, 6 b, androllers 7), above described compression residual stress value, surfacehardness and amount of reduction of surface hardness by heating. Theresults of a test whereby the relationship between the above describedvalues and durability in the rolling/sliding member was verified will beexplained below.

Table 1 below shows specifications of example products according to thisembodiment and comparative example products used for this verificationtest. TABLE 1 Quenching Tempering Ingredient (wt %) temperaturetemperature C Si Cr Mn Mo (° C.) (° C.) Example product 1 1.02 1.48 2.010.45 0.42 860 280 Example product 2 1.05 0.98 3.49 0.43 0.43 900 220Example product 3 0.98 1.53 3.52 0.46 0.42 880 220 Example product 41.01 1.02 4.98 0.44 0.45 920 200 Example product 5 0.99 1.49 4.99 0.450.42 940 220 Example product 6 0.97 2.02 3.47 0.46 0.43 890 250Comparative 0.99 0.98 1.86 0.43 0.44 860 250 Example product 1Comparative 0.98 3.02 2.01 0.45 0.42 860 300 Example product 2Comparative 1.01 0.25 1.46 0.44 0.43 840 200 Example product 3Comparative 1.04 2.98 5.48 0.44 0.44 970 260 Example product 4

These example products (1 to 6) and comparative example products (1 to4) were used for the verification test by using steel adjusted to thepredetermined composition shown in Table 1, conducting quenching andtempering processes under the heat treatment conditions shown in Table1, then applying shot peening treatment to the surface under thefollowing conditions and thereby conducting surface hardening.

The conditions of the above described shot peening treatment are asfollows:

(1) Model (scheme): Direct air compression scheme

(2) Shot particles: RCW06PU (φ0.6 mm) approximately 830 HV

(3) shot peening pressure: 0.49 MPa

(4) Number of revolutions of table (number of revolutions of sample): 12rpm

(5) Nozzle diameter: φ6 mm

(6) Nozzle-sample distance: 100 mm

(7) Arc height: 0.64 mA

(8) Coverage: 200% (target value)

FIG. 3 is a schematic diagram of a durability tester used for thisverification test. In FIG. 3, a durability tester 10 has a disk 11arranged so as to be rotatable around an axis of rotation 13, a pair ofrollers 12 which hold sides 11 a of the disk 11 in the verticaldirection with a predetermined load and a motor M which drives the pairof rollers 12 via a gear box 14 so that the rollers 12 synchronouslyrotate in mutually opposite directions. The disk 11 is constructed so asto be driven to rotate with the torque transmitted from the pair ofrollers 12 driven by the motor M and it is possible to reproduce acondition similar to that of the actual apparatus of transmitting thetorque between an end face 12 a of the roller 12 and the side 11 a ofthe disk 11 and making rolling/sliding contact.

In this verification test, the above described example products andcomparative example products were applied to the disk 11 of thedurability tester 10, a time until rolling and sliding with the roller12 produced breakage on the side 11 a of the disk 11 was measured asuseful life and durability of the disk 11 was evaluated based on theuseful life. The test conditions of the above described durabilitytester 10 were set as follows:

(1) Rotation speed of roller: 3000 rpm

(2) Slip ratio between roller and disk: 14%

(3) Maximum contact pressure: 4.2 GPa

(4) Lubricant: Traction oil for toroidal continuously variabletransmission

(5) Oil film parameter (A): 1.8

Table 2 shows the results of the above described durability test. TABLE2 After shot peening After (after surface hardening) quenching/temperingAmount of Amount of Amount of reduction of Maximum value Surfaceresidual Surface residual surface hardness of residual Useful hardnessaustenite hardness austenite after heating compression life (HRC) (wt %)(HRC) (wt %) (HRC) stress (MPa) (h) Example product 1 61.2 12 62.7 7 0.6950 900 Example product 2 60.8 19 63 10 0.4 1090 1150 Example product 360.9 13 63.6 5 0.3 1040 1020 Example product 4 61.3 15 63 10 0.5 7501200 Example product 5 61.5 17 62.9 11 0.4 980 986 Example product 661.3 14 63.5 5 0.3 1020 1080 Comparative 61 10 61.5 8 1.1 200 452Example product 1 Comparative 61 11 62 7 0.5 500 420 Example product 2Comparative 59 4 62.8 1 2.5 1320 300 Example product 3 Comparative 61 2161 21 0.3 150 484 Example product 4

In addition to the useful life measured by the above describeddurability tester, Table 2 also shows the measurement results of surfacehardness and amount of retained austenite after a quenching/temperingprocess, surface hardness and amount of retained austenite, compressionresidual stress on the surface and amount of reduction of surfacehardness after heating for two hours at 300° C. after shot peeningtreatment of products according to different embodiments and comparativeexamples.

Table 2 shows the amount of reduction of surface hardness after heatingas a difference in surface hardness before and after heating obtained byheating the respective example products and comparative example productswhich have been subjected to shot peening treatment to 300° C., keepingthose products in an atmospheric furnace or the like for two hours andthen measuring surface hardness on the C scale of Rockwell hardness.

As is clear from Table 2, it is appreciated that the useful life in theverification test on the example products according to the presentinvention is approximately double that of the comparative products. Fromthis result, it has been confirmed that the example products accordingto this embodiment have such high fatigue resistance to rolling andsliding that breakage like surface flaking is not produced for a longtime and are provided with high durability.

FIG. 4 is a graph showing a relationship between the amount of Si andthe amount of Cr contained in steel of the respective example productsand comparative example products. In FIG. 4, the horizontal axis shows aweight % value of Si in steel, the vertical axis shows a weight % valueof Cr in steel, and the example products are plotted with white outlinecircles and the comparative example products are plotted with blacksolid circles.

In the figure, in the case of the example products, the amount of Si insteel is set to 1 to 2 wt % and the amount of Cr is set to 2 to 5 wt %,and therefore they are plotted within the range shown by a dotted line Hin the figure. On the other hand, in the case of the comparative exampleproducts, for example, with a circle M1 in the figure (comparativeexample product 1), the amount of Si is substantially 1 wt %, whichsatisfies the above described condition of the amount of Si but theamount of Cr is slightly lower than 2 wt %, which does not satisfy theabove described condition of the amount of Cr. Furthermore, with acircle M2 in the figure (comparative example product 2), the amount ofCr is substantially 2 wt %, which satisfies the above describedcondition of the amount of Cr, but the amount of Si is 3 wt %, whichdoes not satisfy the condition of the amount of Si. In this way, it isunderstandable that the rolling/sliding member needs to satisfyconditions for both the amount of Si and the amount of Cr in steel.

As is evident from the above described results of the verification test,the rolling/sliding member of the present invention uses steelcontaining the above described predetermined contents of Si, Cr,achieves predetermined surface hardness through quenching/tempering,applies the above described surface compression residual stress, and canthereby keep surface hardness necessary for the rolling/sliding membereven when the surface of the rolling/sliding member is heated with heataccompanying rolling and sliding and suppress generation of surfacecracks caused by a reduction of surface hardness. In addition to theeffect of improving fatigue resistance due to surface compressionresidual stress, it is also possible to more effectively increasefatigue resistance of the rolling/sliding member and achieve higherdurability.

This result shows that the effects become conspicuous in a full toroidalcontinuously variable transmission whose contact part between the rollerand the disk is accompanied by large amount of spin and which is putunder difficult contact conditions.

That is, the toroidal continuously variable transmission according tothis embodiment applies rolling/sliding members with enhanced fatigueresistance and higher durability, and can thereby further increase thedurability.

Furthermore, according to the method of manufacturing therolling/sliding member of the above described embodiment, not only usingthe heat-resistant bearing steel but also including thequenching/tempering process and the surface hardening process caneffectively increase fatigue resistance and obtain rolling/slidingmembers with higher durability.

The rolling/sliding member of the present invention is not limited tothe above described embodiment. For example, the above describedembodiment applies the rolling/sliding member according to the presentinvention to all the input/output disks and rollers of the toroidalcontinuously variable transmission, but it is also possible to apply therolling/sliding member of the present invention to only the input/outputdisks and combine them with rollers according to other specificationsusing, for example, SUJ2.

Furthermore, the above described embodiment has shown the full toroidalcontinuously variable transmission, but the present invention is alsoapplicable to a toroidal continuously variable transmission in othermodes such as a half toroidal type.

1. A rolling/sliding member used for a toroidal continuously variabletransmission, wherein the rolling/sliding member is made of steelcontaining at least: C: not less than 0.8 wt % and not more than 1.5 wt% Si: not less than 0.9 wt % and not more than 2.1 wt % Cr: not lessthan 2 wt % and not more than 5 wt % wherein by applying surfacehardening through machining to a surface whose surface hardness is setto not less than 60 HRC and not more than 64 HRC throughquenching/tempering, surface compression residual stress thereof is setto not less than 700 MPa and not more than 1100 MPa, and the amount ofreduction of surface hardness when heated at 300° C. is not more than 1HRC.
 2. The rolling/sliding member according to claim 1, wherein theamount of retained austenite before the surface hardening is not lessthan 10 wt % and not more than 20 wt %.
 3. The rolling/sliding memberaccording to claim 1, wherein an austenitizing temperature is not lessthan 870° C. and not more than 950° C. and an tempering temperature isnot less than 200° C. and not more than 280° C.
 4. A method ofmanufacturing a rolling/sliding member used for a toroidal continuouslyvariable transmission, comprising: a quenching/tempering process ofperforming quenching/tempering on an intermediate material of therolling/sliding member made of steel containing at least: C: not lessthan 0.8 wt % and not more than 1.5 wt % Si: not less than 0.9 wt % andnot more than 2.1 wt % Cr: not less than 2 wt % and not more than 5 wt %at an austenitizing temperature of not less than 870° C. and not morethan 950° C. and an tempering temperature of not less than 200° C. andnot more than 280° C. to thereby set surface hardness of theintermediate material to not less than 60 HRC and not more than 64 HRCand the amount of retained austenite to not less than 10 wt % and notmore than 20 wt %; and a surface hardening process of applying surfacehardening through machining to the intermediate material which hasundergone the quenching/tempering process, thereby setting surfacecompression residual stress of the intermediate material to not lessthan 700 MPa and not more than 1100 MPa and setting the amount ofreduction of surface hardness to not more than 1 HRC when heated at 300°C.
 5. A toroidal continuously variable transmission comprising: an inputdisk having a concave curved raceway surface on a side; an output diskhaving a concave curved raceway surface facing the raceway surface ofthe input disk on a side; and rollers which are sandwiched betweenraceway surfaces of the respective disks in a rotatable manner andtransmit torque between the respective disks through rolling and slidingbetween the respective disks, wherein at least one of the input disk,output disk and rollers, which are rolling/sliding members, is therolling/sliding member according to claim
 1. 6. The rolling/slidingmember according to claim 2, wherein an austenitizing temperature is notless than 870° C. and not more than 950° C. and an tempering temperatureis not less than 200° C. and not more than 280° C.